The overall objectives of this research are to develop a unified theory of genetic control that incorporates both nulear and cytoplasmic genetic systems. For this purpose we are using primarily the unicellular eukaryotic microorganism Chlamydomonas as a model system. One specific aim is to characterize the site-specific eukaryotic restriction enzyme we have recently isolated from Chlamydomonas; and to determine its mode of action in this organism. A second aim is to examine the molecular basis of maternal inheritance of chloroplast DNA, by looking for modification and restriction enzyme activities in zygotes of Chlamydomonas. A third aim is to correlate genetic and physical maps of chloroplast DNA, using restriction fragment mapping procedures. A fourth aim is to explore the role of chloroplast and mitochondrial proteins in regulating the synthesis of nuclear DNA and thereby controlling the cell cycle. BIBLIOGRAPHIC REFERENCES: Sager, Ruth (1976) Cytoplasmic inheritance, Chapter 7 in Cell Biology: A Comprehensive Treatise (L. Goldstein and D. Prescott, eds.) Academic Press, Inc., New York, in press. Burton, William G., R.J. Roberts, P.A. Myers, and R. Sager (1977) A site specific single strand endonuclease from the eukaryote Chlamydomonas. Proc. Nat. Acad. Sci. USA. in press.